This invention relates generally to aneroid pressure gauges or barometers and, more particularly, to aneroid pressure gauges wherein changes in pressure are indicated by changes in capacitance resulting from the deflection of the membranes which define the evacuated capsule or cell forming a component of the pressure gauge. Aneroid pressure gauges are known which measure pressure by means of changes in the capacitance of associated components effected by the deflection of one of the membranes of the aneroid capsule forming a component of the pressure gauge. Thus, in one existing aneroid pressure gauge, an aneroid capsule or cell comprising a pair of membranes defining a sealed evacuated space between them has one of these membranes fastened to the chassis or housing of the pressure gauge. A capacitor is provided including one fixed capacitor plate and an opposed movable capacitor plate. The movable membrane of the aneroid capsule is fastened to the movable capacitor plate so that changes in pressure result in a deflection of the capsule membrane which, in turn, results in a corresponding movement of the movable capacitor plate thereby changing the capacitance of the capacitor. Thus, it is the output of the capacitor which is measured in order to obtain pressure measurements. Such capacitance type aneroid pressure gauges are particularly useful in connection with radiosondes which, among other things, measure minute changes in pressure over short intervals of time.
Aneroid pressure gauges of the type described above are not entirely satisfactory, however. Thus, the dielectric coefficient of the air gap between the capacitor plates of the above-described conventional aneroid pressure gauges is influenced by the moisture present in the ambient air as well as the ambient pressure and temperature. The influence of the ambient moisture, pressure and temperature on the dielectric coefficient of the air gap results in a non-linearity between the pressure and capacitance variations thereby resulting in measuring errors.